Abstract

Development of late-mature topography has removed nearly all Kansan drift from extensive areas in northwestern Missouri, and the present land surface bevels the Nebraskan gumbotil horizon. In north-central Missouri, the Grand River and its larger tributaries have cut through the Kansan deposits, developing a pronounced digitate boundary between the two drifts and leaving numerous Kansan outliers on the higher divides. Kansan gumbotil caps extensive tabular divides east of the Chariton River valley, but many of the deeper intervening valleys expose inliers of Nebraskan drift. In places, the bedrock surface lies higher than the adjacent Nebraskan gumbotil horizon.

Kansan drift apparently overlaps the Nebraskan to the southeast, though present data are inadequate for accurate age determination along much of the glacial boundary.

At some localities the Aftonian horizon is marked by sandy and gravelly silts presumably of fluvial origin. Similar materials of widespread occurrence beneath the Kansan drift rest on bedrock and may be preglacial.

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